1. Field of the Invention
This invention relates to achieving more energy-efficient horizontal motion of a two-member knuckle boom, especially but not necessarily those which carry a tree-working tool at the distal end thereof. The term “tree-working tool” throughout this specification is intended to encompass, for example, saw heads and other devices (such as shear heads, for example), for cutting trees at the stump; tree delimbing heads; tree processing heads; wood-handling grapples for piling or loading trees or logs; and other such tools in the tree-harvesting industry. However, it is emphasized that the invention is not limited to knuckle booms used in the tree-harvesting industry.
A typical two-member knuckle boom comprises a hoist boom having a proximal end pivoted to the machine base, and a stick boom having a proximal end pivoted to the distal end of the hoist boom. In the tree-harvesting industry, a tree-working tool such as a disc saw head would be mounted on the distal end of the stick boom. Other industries of course will use other tools. A hoist cylinder is mounted between the machine base and the hoist boom, and a stick cylinder is mounted between the hoist boom and the stick boom.
2. Description of the Prior Art
The invention expands on the concepts described and claimed in Canadian patent no. 2,317,670, granted Jul. 16, 2002, and in corresponding U.S. Pat. No. 6,443,196, granted Sep. 3, 2002 (hereinafter referred to as “the prior Kurelek patents”). The prior Kurelek patents explained the concept of a hydraulic circuit for a knuckle boom which provides connecting hydraulic lines between the working ends of the hoist and stick cylinders, providing an oil flow so as to enable shunting of hydraulic oil between the working ends of the cylinders. When these cylinders are alternately extending and contracting during reaching actions with the knuckle boom, such as is always a part of tree harvesting, the circuit in that invention shunts load-supporting hydraulic oil between the cylinders rather than dumping it to tank as with previous conventional circuits. This has resulted in reduced working horsepower, i.e. fuel used and heat generation, and the ability of the operator to do reaching and tucking by operating just one lever, while continuing to do lifting and lowering with the other. This is explained in detail in the prior Kurelek patents.
In the prior Kurelek patents, there was no direct control of the shunting of hydraulic oil, for example via a valve or pump. Instead, the “reach” movement of the boom (i.e. generally horizontal extension or retraction) was controlled by an additional hydraulic cylinder, acting as a “reach” cylinder, mounted between the hoist and stick booms. In one sense, the reach cylinder in effect controlled or constrained the shunting of oil between the working ends, since the reach cylinder determined the relative positions of the hoist and stick cylinders. The reach cylinder operates one of the knuckle boom angles, usually working alongside the stick cylinder, and causes the load supporting oil to flow back and forth between the hoist and stick cylinders. The reach cylinder is required to provide the horizontal push and pull forces at the tool but normally does not do major load supporting work.
In practice, tree harvesting machines with the concepts of the prior Kurelek patents do function with benefits as described, and have already become well-accepted by users. Thus some users want to retrofit existing conventional machines to incorporate the invention, but that is difficult because the addition of a reach cylinder means that lugs for its mounting must be provided during manufacture of the machine, and on some knuckle boom structures there is insufficient physical space for a reach cylinder unless other major components are repositioned.
There is thus an ongoing need for circuits that will provide the benefits of the prior Kurelek patents without necessarily needing the major extra lugging construction and additional cylinder, and for other variations and improvements as well.